Advancements in communication technologies have permitted the implementation of mobile communication systems, such as a cellular communication system. Telephonic communication, of both voice and data, is generally possible through the use of a mobile communication system.
Communication by way of a mobile communication system is advantageous as communications can be effectuated by way of a mobile station carryable by a user. Improved mobility of communications is possible as a wireline connection is not required to form a communication link.
Telephonic communications effectuated by use of a cellular communication system, as well as various other types of mobile communication systems, appear to a user generally to be similar to those effectuated by way of a conventional, wireline telephonic network.
However, the mobile nature of a mobile communication system prevents simple tracking of the location at which a call is placed, such as a call for emergency assistance by a user of a mobile station operable in such a system.
When a call is originated at a conventional wireline device, the geographical position from which the call is originated is easily determinable. A simple mapping between the telephonic identity of the originating, wireline device and the location at which the device is installed, indicates the geographical positioning of the originating party. In contrast, because of the inherent mobility permitted of a mobile station, a subscriber of a mobile station is able to originate a call with the mobile station at almost any location within a geographical area encompassed by the cellular communication system. The geographical position at which the call is originated is, therefore, not easily determinable. Determination of the location at which a call is originated is vitally important, for instance, in a request for emergency assistance. If a request for emergency assistance is made by way of a mobile station and the originating party is unable to indicate to emergency personnel the location from which the request for emergency assistance is made, delivery of the emergency assistance might be, at the least, delayed.
Proposals have been set forth to overcome this shortcoming of use of a radio communication system. One such proposal makes use of GPS (global positioning system) technologies. GPS receivers are available to receive and detect TOA- (time-of-arrival) signals generated by satellite based transmitters (the "satellites"). Three signals received from three separate satellites at a GPS receiver are used by the GPS receiver to determine an accurate 3D (three dimensional) geographic positioning of the GPS receiver if the GPS receiver is synchronized to the satellites. Incorporation of GPS receiver circuitry in a mobile station permits the geographical positioning of the mobile station to be determinable. And, such incorporation, is proposed to overcome the inability to automatically determine the physical positioning of a mobile station.
Accurate position determination utilizing GPS techniques, however, requires the detection of three separate TOA-signals delivered directly, i.e., by line-of-sight from the three satellite-based, or other, transmitters. The GPS receiver, or mobile station incorporating circuitry capable of detecting TOA-signals, such as those generated by satellite-based transmitters, might be positioned at a location, or otherwise be operated in a non-ideal propagation environment, in which three line-of-sight TOA-signals cannot be detected. For instance, in an urban area, topographical features, such as building structures, might prevent line-of-sight detection of a TOA-signal. Instead, only non-line-of-sight (NLOS) detection might be possible. Also, only two TOA-signals, or perhaps only a single TOA-signal, might be detectable. Conventional GPS techniques do not compensate for NLOS conditions, or for the determination of a location fix if only two TOA-signals are detectable.
A manner by which to determine the geographical position of a wireless communication station when operated in a non-ideal propagation environment would be advantageous.
It is in light of this background information related to determination of geographic positioning of a wireless communication station that the significant improvements of the present invention have evolved.